Enhanced oil recovery (EOR) refers to techniques for increasing the amount of petroleum which can be produced from an oil reservoir. Water injection or waterflooding has been used as a method for reservoir management, helping to maintain reservoir pressure and enhance production of hydrocarbon reserves. Because of the structure of the reservoir and relative inter-facial tensions involved, the flood water may form channels or fingers, bypassing the oil in the formation. Even where water has flowed, residual oil is trapped in pores by viscous and capillary forces. Further flooding with water will not remove such oil.
Surfactant flooding to recover oil has been actively investigated due to the relatively poor ability of water floods to displace remaining oil from a reservoir's pore structure. The use of surfactants has been limited due to both availability (including relatively complex manufacturing processes) and high cost of the surfactants. This makes surfactant flooding systems for oil recovery generally expensive with high front end cost loads.
Surfactant compositions for use in the prior art employed a petroleum sulfonate as either the sole surfactant, or at least a major component of a mixture of surfactants. Synthetic alkyl benzene sulfonates, alkyl sulfonates and sulfates have also been used as oil recovery surfactants. To combat separation problems in surfactant mixtures, especially at high salinities (>2% salt), a surfactant with both water soluble and oil soluble characteristics was often added to sulfonate surfactant mixtures. These materials were referred to as “solubilizers” and were usually sulfate or sulfonate salts of polyethoxylated alcohols or alkylphenols.
Conversion of lignin, i.e., wood based materials, into surfactants by reduction reactions and their use in chemical flood systems in EOR has been described in U.S. Pat. Nos. 4,739,040, and 6,100,385, incorporated herein by reference. The methods consist of reducing the lignin into a lignin bio-oil which is a complex product mixture of phenols. The lignin bio-oil can then be modified chemically to form water soluble surfactants by one or a combination of several chemical reactions such as alkoxylation, alkylation, sulfonation, sulfation, and sulfomethylation. Other chemical modifications have been developed to modify the surfactant properties of the lignin bio-oil surfactants, as disclosed in U.S. Pat. Nos. 5,095,985; 5,095,986; 5,230,814; and 5,035,288, also incorporated herein by reference.
There is still a need for improved methods for making surfactant compositions based on natural resources such as wood and plants, and improved surfactant compositions derived from such natural resources.